JP2016029745A - Bonding capillary - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase joint strength while suppressing the occurrence of cracks in a bonding wire, in a bonding capillary.SOLUTION: A bonding capillary according to an embodiment includes: a pressing surface pressing a bonding wire; an insertion hole through which the bonding wire is inserted; a tapered hole communicating the insertion hole with the pressing surface and expanding toward the pressing surface; and a chamfered portion provided between the tapered hole and the pressing surface. The chamfered portion has an irregular profile on a surface thereof, and the sharpness of projecting portions at the irregular profile is lower than that of recessed portions at the irregular profile.SELECTED DRAWING: Figure 7

Description

  The disclosed embodiments relate to bonding capillaries.

  Conventionally, wire bonding is known as one method for electrically connecting a semiconductor chip and a lead frame. Wire bonding is a method of electrically connecting metal wires called bonding wires between semiconductor chips and lead frame electrodes.

  In wire bonding, a cylindrical tool called a bonding capillary is used. Specifically, the bonding wire is projected from the tip through the bonding wire, and the protruding bonding wire is pressed against the electrode using the tip surface of the bonding capillary. Further, the bonding wire is rubbed against the electrode by applying ultrasonic waves to the bonding capillary to vibrate the tip surface. Thereby, the bonding wire is bonded to the electrode.

  Known bonding capillaries are provided with an R portion having a predetermined curvature at the periphery of the opening of an insertion hole through which the bonding wire is inserted in order to prevent the bonding wire from adhering to the tip surface (for example, a patent) Reference 1).

Japanese Patent Laid-Open No. 9-326411

  However, when wire bonding is performed using the above-described bonding capillary having the R portion, there is a problem that it is difficult to obtain bonding strength. This is because the provision of the R portion reduces the gripping force against the bonding wire and makes it difficult to rub the bonding wire against the electrode.

  Such a problem of bonding strength becomes prominent when wire bonding is performed using an Al (aluminum) bonding wire. This is because, compared to Au (gold) generally used as a material for bonding wires, Al is easily oxidized, and the oxide film formed on the surface tends to hinder the bonding with the electrode.

  In addition, the bonding wire made of Al has a problem that cracks are likely to occur compared to the bonding wire made of Au. Therefore, when wire bonding is performed using an Al bonding wire, it is preferable to increase both the bonding strength and suppress the generation of cracks.

  An object of one embodiment is to provide a bonding capillary that can increase the bonding strength while suppressing the occurrence of cracks in the bonding wire.

  A bonding capillary according to an aspect of the embodiment communicates a pressing surface that presses a bonding wire, an insertion hole through which the bonding wire is inserted, the insertion hole and the pressing surface, and widens toward the pressing surface. A tapered hole, and a chamfered portion provided between the tapered hole and the pressing surface, the chamfered portion has a concavo-convex shape on the surface, and the degree of sharpness of the convex portion in the concavo-convex shape is The degree of sharpness of the concave portion in the concave-convex shape is smaller.

  Since the chamfered portion is provided between the tapered hole and the pressing surface, the stress applied to the bonding wire can be relaxed, so that the occurrence of cracks in the bonding wire can be suppressed. Moreover, since the gripping force with respect to the bonding wire when the bonding wire is rubbed against the electrode can be improved by providing an uneven shape on the surface of the chamfered portion, the bonding strength can be increased. On the other hand, if the concavo-convex shape is simply provided, the wire may be damaged by the sharpness of the convex portion in the concavo-convex shape, and there is a possibility that a crack is likely to occur in the wire due to this flaw. Therefore, the degree of sharpness of the convex part in the concavo-convex shape is made smaller than the degree of sharpness of the concave part. Thereby, generation | occurrence | production of the crack resulting from uneven | corrugated shape can be suppressed.

  Further, the uneven shape of the chamfered portion is characterized in that the skewness is −0.164 or less and the average height is 0.035 μm or more and 0.092 μm or less.

  Thereby, when performing wire bonding using the bonding wire made from Al, generation | occurrence | production of the crack to the bonding wire after a 1st bonding process can be suppressed suitably. In addition, sufficient bonding strength can be obtained at the tail portion after the second bonding step.

  The pressing surface has an uneven shape, and the degree of sharpness of the convex portion in the uneven shape of the pressing surface is larger than the degree of sharpness of the convex portion in the uneven shape of the chamfered portion.

  The pressing surface is less likely to cause cracks in the bonding wire than the chamfered portion. For this reason, it is good also as the said structure from a viewpoint which attaches importance to the improvement of grip power rather than generation | occurrence | production of a crack in a press surface. By setting it as the said structure, the grip force with respect to a bonding wire can further be improved.

  The uneven shape on the pressing surface has an average height of 0.113 μm or more.

  Thereby, when wire bonding is performed using an Al bonding wire, a sufficient bonding strength can be obtained at the stitch portion after the second bonding step.

  Further, the chamfered portion has a curved surface that is smoothly continuous with the tapered hole and the pressing surface, and the curvature radius of the curved surface is 4.55 μm or more and 20.30 μm or less.

  Thereby, when performing wire bonding using the bonding wire made from Al, generation | occurrence | production of the crack to a bonding wire can be suppressed suitably. In addition, it is possible to suitably suppress the occurrence of defective bonding of the bonding wire after the second bonding process.

  Further, the chamfered portion has a curved surface that is smoothly continuous with the tapered hole and the pressing surface, and the curvature radius of the curved surface is 12.8 μm or more and 20.30 μm or less.

  Thereby, when performing wire bonding using an Al bonding wire, even if the loop length of the bonding wire is 3 mm or more, occurrence of cracks in the bonding wire can be suitably suppressed. In addition, it is possible to suitably suppress the occurrence of defective bonding of the bonding wire after the second bonding process.

  The taper angle of the tapered hole is 100 ° or less.

  Thereby, generation | occurrence | production of the crack to a bonding wire can be suppressed suitably in the boundary corner | angular part of the said insertion hole and the said taper-shaped hole.

  The outer diameter of the pressing surface may be 4.0 times or more and 5.7 times or less the wire diameter of the bonding wire.

  Thereby, desired joining strength can be obtained.

  According to one aspect of the embodiment, the bonding strength can be increased while suppressing the occurrence of cracks in the bonding wire.

FIG. 1 is a schematic side view showing a bonding capillary according to this embodiment. FIG. 2 is a schematic enlarged view of a portion H1 shown in FIG. FIG. 3 is a schematic cross-sectional side view showing the tip portion of the bottleneck portion. FIG. 4 is a schematic enlarged view of a portion H2 shown in FIG. FIG. 5 is a schematic side sectional view showing the surface shape of the pressing surface. FIG. 6 is a schematic side sectional view showing the surface shape of the chamfered portion. FIG. 7 is a schematic side sectional view showing a state of the first bonding step. FIG. 8 is a schematic side sectional view showing a state of the second bonding step. FIG. 9 is a graph illustrating a surface roughness curve of a chamfered portion. FIG. 10 is a diagram showing the evaluation results when the skewness and average height of the uneven shape in the chamfered portion and the average height of the uneven shape on the pressing surface are respectively changed. FIG. 11 is a diagram showing an evaluation result when the curvature radius of the chamfered portion is changed. FIG. 12 is a diagram showing an evaluation result when the curvature radius of the chamfered portion is changed. FIG. 13 is a diagram showing an evaluation result when the angle of the tapered hole is changed. FIG. 14 is a schematic perspective view showing an example of a bonding simulation result. FIG. 15 is a schematic plan view showing an example of a bonding simulation result. FIG. 16 is a diagram showing the evaluation results when the ratio between the outer diameter of the pressing surface and the wire diameter is changed. FIG. 17 is a flowchart illustrating a part of the manufacturing method of the bonding capillary.

  Hereinafter, embodiments of a bonding capillary disclosed in the present application will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

(Embodiment)
First, the overall configuration of the bonding capillary according to the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic side view showing a bonding capillary according to this embodiment. FIG. 2 is a schematic enlarged view of a portion H1 shown in FIG.

  As shown in FIG. 1, a bonding capillary 1 (hereinafter referred to as “capillary 1”) according to this embodiment has an insertion hole 11 through which a bonding wire (hereinafter referred to as “wire”) is inserted. The capillary 1 is made of, for example, ceramic. Examples of the material of the capillary 1 include alumina. Alternatively, the material of the capillary 1 includes a composite material containing alumina and at least one of zirconia and chromia.

  The capillary 1 includes a cylindrical part 12, a conical part 13, and a bottleneck part 14. The conical part 13 is a part provided at one end of the cylindrical part 12, and has a shape that decreases in diameter toward the tip side. The bottle neck part 14 is a part provided at the tip of the cone part 13, and has a smaller diameter than the tip diameter of the cone part 13. The insertion hole 11 is provided so as to penetrate the cylindrical portion 12, the conical portion 13, and the bottle neck portion 14.

  As shown in FIG. 2, a tapered hole 20 is provided between the pressing surface 30 that is the distal end surface of the bottle neck portion 14 and the insertion hole 11. The tapered hole 20 is tapered so as to increase in diameter from the insertion hole 11 toward the pressing surface 30.

  In the capillary 1 configured as described above, the wire protruding outward from the tapered hole 20 is pressed against the electrode using the pressing surface 30, and the pressing surface 30 is vibrated by ultrasonic waves to rub the wire against the electrode. Bond the wire to the electrode.

  Here, Au (gold) is generally used as the material of the wire. On the other hand, Al (aluminum) is generally used for a pad electrode which is an electrode of a semiconductor chip. When Au and Al, which are dissimilar metals, are bonded in this way, voids are generated at the bonding interface, and the bonding strength may be reduced. Moreover, there is a problem that the manufacturing cost of the semiconductor device is increased by using expensive Au.

  For this reason, in recent years, it has been proposed to use Al, which is the same material as the pad electrode of the semiconductor chip and is cheaper than Au, as the wire material.

  However, Al has a lower strength than Au. For this reason, after the first bonding process described later, there is a problem that cracks are likely to occur in the bent portion of the wire. Further, Al is more easily oxidized than Au, and the bonding with the electrode is likely to be hindered by the oxide film formed on the surface. For this reason, there also exists a problem that it is not easy to obtain sufficient joint strength.

  Therefore, in the capillary 1 according to the present embodiment, the chamfered portion is provided at the boundary portion between the pressing surface 30 and the tapered hole 20 to suppress the occurrence of cracks in the bent portion of the wire. Further, in the capillary 1 according to the present embodiment, by providing a fine uneven shape in the chamfered portion, the gripping force to the wire when the pressing surface 30 is vibrated and the wire is rubbed against the electrode is improved. It was decided to increase.

  On the other hand, if the concavo-convex shape is simply provided, the wire may be damaged by the sharpness of the convex portion in the concavo-convex shape, and the wire may be easily cracked due to the damage. For this reason, in the capillary 1 according to the present embodiment, the degree of sharpness of the convex part in the concave-convex shape is made smaller than the degree of sharpness of the concave part. Thereby, generation | occurrence | production of the crack resulting from uneven | corrugated shape can be suppressed. The “degree of sharpness” means the degree of sharpness of the convex part and the concave part. Therefore, “making the sharpness of the convex portion smaller than the sharpness of the concave portion” means that the sharpness of the convex portion is made gentler than the sharpness of the concave portion.

  Below, the structure of the chamfered part formed in the boundary part of the press surface 30 and the taper-shaped hole 20, and the uneven shape formed in the surface of a chamfered part is demonstrated concretely with reference to FIG. 3 and FIG. FIG. 3 is a schematic side cross-sectional view showing the tip portion of the bottleneck portion 14. FIG. 4 is a schematic enlarged view of a portion H2 shown in FIG.

  As shown in FIG. 3, the pressing surface 30 is formed in a convex shape that slightly protrudes from the outer edge toward the center. Further, the tapered hole 20 is formed in the central portion of the pressing surface 30. Therefore, in the capillary 1, the boundary portion between the tapered hole 20 and the pressing surface 30 is a portion that protrudes to the most distal end side, and a crack is easily generated in the wire in this portion.

  The chamfered portion 40 is provided at a boundary portion between the tapered hole 20 and the pressing surface 30. As shown in FIG. 4, the chamfered portion 40 has a curved surface that continues smoothly from the tapered hole 20 to the pressing surface 30.

  FIG. 5 is a schematic side sectional view showing the surface shape of the pressing surface 30. FIG. 6 is a schematic side sectional view showing the surface shape of the chamfered portion 40. As shown in FIGS. 5 and 6, the pressing surface 30 and the chamfered portion 40 are formed with fine uneven shapes on the surface. Each of these concavo-convex shapes is formed such that the degree of sharpness of the convex parts 31 and 41 is smaller than the degree of sharpness of the concave parts 32 and 42.

  Further, the uneven shape of the pressing surface 30 shown in FIG. 5 is formed such that the degree of sharpness of the convex portion 31 is larger than the degree of sharpness of the convex portion 41 in the uneven shape of the chamfered portion 40 shown in FIG. Thereby, in the capillary 1 according to the present embodiment, the grip force of the pressing surface 30 on the wire is higher than the grip force of the chamfered portion 40 on the wire.

  Next, the operation of the above configuration will be described with reference to FIGS. 7 and 8 together with the wire bonding operation. FIG. 7 is a schematic side sectional view showing a state of the first bonding step. FIG. 8 is a schematic side sectional view showing the state of the second bonding step.

  The wire bonding includes a first bonding process, a loop forming process, and a second bonding process. The first bonding step is a step of bonding a wire to one electrode. The loop forming step is a step of forming a wire loop between the electrodes by moving the capillary 1 along a predetermined trajectory after the first bonding step. The second bonding step is a step of bonding a wire to the other electrode after the loop formation step. Through these steps, wires are bridged between the electrodes, and the semiconductor chip and the lead frame are electrically connected.

  FIG. 7 shows a case where wire bonding is performed using an Al wire (hereinafter referred to as “Al wire”) instead of a conventional Au wire (hereinafter referred to as “Au wire”). The state of the first bonding process is shown.

  Here, in wire bonding using a conventional Au wire, ball bonding is performed as a first bonding step. Ball bonding is a method in which the tip of a wire is melted by discharge to form an Au ball, and this ball is bonded to the electrode by thermocompression bonding. A bonding capillary is used for ball bonding.

  On the other hand, when wire bonding is performed using an Al wire, it is difficult to perform the above-described ball bonding. This is because Al is easier to oxidize than Au and it is difficult to form a ball like Au. For this reason, when performing wire bonding using an Al wire, a wedge bonding tool for bonding a wire to an electrode without forming a ball is generally used (see, for example, Japanese Patent Laid-Open No. 2001-156100).

  However, the wedge bonding tool is expensive and has a low durability because of its complicated structure as compared with the bonding capillary. For this reason, in this embodiment, wire bonding using an Al wire is performed using the capillary 1 which is a bonding capillary that is cheaper and more durable than the wedge bonding tool. Thereby, the productivity of the semiconductor device can be increased.

  As shown in FIG. 7, the capillary 1 first presses the Al wire W against one electrode, for example, the lead electrode 100 of the lead frame, using the pressing surface 30. At this time, a predetermined interval is provided between the chamfered portion 40 and the lead electrode 100 so that the Al wire W is not divided between the chamfered portion 40 and the lead electrode 100.

  Subsequently, an ultrasonic wave is applied to the cylindrical portion 12 (see FIG. 1) of the capillary 1. Thereby, the pressing surface 30 vibrates and the Al wire W is rubbed against the lead electrode 100. Thereby, the Al wire W is bonded to the lead electrode 100.

  Subsequently, the capillary 1 moves while drawing a predetermined trajectory, thereby forming a wire loop. At this time, a bent portion is formed at the boundary between the portion joined to the lead electrode 100 of the Al wire W and the portion not joined, for example, the region B shown in FIG. Cracks are likely to occur at the bent portion.

  As a countermeasure against this point, in the capillary 1 according to the present embodiment, a chamfered portion 40 is provided at a boundary portion between the tapered hole 20 and the pressing surface 30. Thereby, compared with the case where the chamfered portion 40 is not provided, the stress concentration in the region B is alleviated, so that the occurrence of cracks at the bent portion of the Al wire W can be suppressed.

  In addition, as described above, the Al wire W has a problem that it is not easy to obtain sufficient bonding strength compared to the Au wire because the bonding with the electrode is easily hindered by the oxide film formed on the surface. .

  As a countermeasure against this point, in the capillary 1 according to the present embodiment, a fine uneven shape is provided on the surface of the chamfered portion 40. Thereby, since the grip force with respect to the Al wire W of the chamfered portion 40 is improved, a sufficient bonding strength can be obtained even when the Al wire W in which the bonding strength is difficult to be obtained as compared with the Au wire is used.

  The uneven shape of the chamfered portion 40 is formed such that the degree of sharpness of the convex part 41 is smaller than the degree of sharpness of the concave part 42. For this reason, according to the capillary 1 according to the present embodiment, high bonding strength can be obtained while suppressing the occurrence of cracks due to the uneven shape.

  In the capillary 1 according to this embodiment, the pressing surface 30 is also provided with a fine uneven shape. The pressing surface 30 is less likely to cause a crack in the Al wire W than the chamfered portion 40. For this reason, from the viewpoint of emphasizing the improvement of the grip force rather than preventing the occurrence of cracks, the concavo-convex shape of the pressing surface 30 is such that the degree of sharpness of the convex part 31 is higher than the degree of sharpness of the convex part 41 in the concave-convex shape of the chamfered part 40 It is formed to be large (see FIGS. 5 and 6). Thereby, the grip force with respect to the Al wire W can be further improved.

  Subsequently, the capillary 1 performs a second bonding process. First, as shown in FIG. 8, the capillary 1 presses the Al wire W against the other electrode, for example, the pad electrode 200 of the semiconductor chip, using the pressing surface 30. In the second bonding process, the Al wire W needs to be divided after the Al wire W is bonded to the pad electrode 200. For this reason, the interval between the chamfered portion 40 and the pad electrode 200 is set shorter than that in the first bonding step.

  Subsequently, the capillary 1 vibrates the pressing surface 30 with ultrasonic waves and rubs the Al wire W against the pad electrode 200. Thereby, the Al wire W is bonded to the pad electrode 200.

  Subsequently, the capillary 1 is raised by a predetermined distance. At this time, as shown in FIG. 8, the Al wire W is bonded to the pad electrode 200 not only in the stitch portion S outside the chamfered portion 40 but also in the tail portion T inside the chamfered portion 40. It has become. For this reason, when the capillary 1 rises, the Al wire W is pulled out from the capillary 1 with this rise. The drawn Al wire W becomes a part to be joined to the lead electrode 100 in the next first bonding process.

  Thereafter, for example, when the capillary 1 moves to the left and right, the Al wire W is divided between the stitch portion S and the tail portion T.

  Thus, in the second bonding step, in order to draw the Al wire W from the capillary 1, it is necessary to temporarily bond the Al wire W to the pad electrode 200 in the tail portion T. However, as described above, since an oxide film is easily formed on the Al wire W, it is not easy to ensure the bonding strength of the tail portion T.

  On the other hand, in the capillary 1 according to the present embodiment, the gripping force of the chamfered portion 40 against the Al wire W is improved by providing the chamfered portion 40 with a fine uneven shape. Bonding strength can be obtained.

  As described above, the capillary 1 according to this embodiment includes the pressing surface 30, the insertion hole 11, the tapered hole 20, and the chamfered portion 40. The pressing surface 30 is a surface that presses the bonding wire. The insertion hole 11 is a hole through which the bonding wire is inserted. The tapered hole 20 is a hole that connects the insertion hole 11 and the pressing surface 30, and has a shape that widens toward the pressing surface 30. The chamfered portion 40 is provided between the tapered hole 20 and the pressing surface 30. The chamfered portion 40 has a concavo-convex shape on the surface, and the degree of sharpness of the convex portion 41 in the concavo-convex shape is smaller than the degree of sharpness of the concave portion 42 in the concavo-convex shape.

  Therefore, according to the capillary 1 according to the present embodiment, the bonding strength can be increased while suppressing the occurrence of cracks in the bonding wire.

(Example)
Next, examples of the capillary 1 according to this embodiment will be described with reference to FIGS. FIG. 9 is a graph illustrating a surface roughness curve of a chamfered portion. FIG. 10 is a diagram showing evaluation results when the skewness and average height of the uneven shape in the chamfered portion 40 and the average height of the uneven shape in the pressing surface 30 are changed. FIG. 11 is a diagram showing an evaluation result when the radius of curvature of the chamfered portion 40 is changed.

  The uneven shape of the pressing surface 30 and the chamfered portion 40 is represented by, for example, an average height Rc and a skewness Rsk. The average height Rc and the skewness Rsk are calculated based on JIS B 0601-2001.

  The skewness Rsk is a value representing the symmetry between the convex part and the concave part in the concavo-convex shape. If the uneven shape is symmetrical, the skewness Rsk is zero. In addition, when the skewness Rsk is negative, the degree of sharpness of the convex part in the concave-convex shape is smaller than the degree of sharpness of the concave part, in other words, the area of the tip part of the convex part when the concave-convex shape is viewed in plan is the bottom of the concave part. It means larger than the area of the part.

In the present embodiment, the roughness curves of the pressing surface 30 and the chamfered portion 40 were measured using a laser microscope (OLYMPUS, OLS4000). The measurement conditions are as follows.
Measurement magnification: 50 times Evaluation length (roughness measurement): 500 μm to 800 μm
Cut-off (phase compensation type high-pass filter) λc: 25 μm

  From the roughness curve measured under the above conditions, the average height Rc was determined by the following equation (1), and the skewness Rsk was determined by the following equation (2).

  Here, in Expression (1), m is the number of contour curve elements, and Zti is the average value of the heights of the contour curve elements. Moreover, in Formula (2), Zq is a root mean square height, Zn is the height value in a roughness curve.

  An example of the roughness curve obtained by measuring the surface of the chamfered portion 40 with a laser microscope is as shown in FIG. In FIG. 9, the vertical axis represents the height (micrometer: μm), and the horizontal axis represents the measurement position (μm). In the roughness curve shown in FIG. 9, the skewness Rsk of the uneven shape of the chamfered portion 40 is −0.164, and the average height Rc of the uneven shape of the chamfered portion 40 is 0.073.

  FIG. 10 shows items of “crack”, “tail joint”, and “stitch joint” when the skewness Rsk and average height Rc of the chamfered portion 40 and the average height Rc of the pressing surface 30 are changed. The evaluation results are shown.

  Here, the “crack” item is an item indicating whether or not a crack has occurred in the Al wire W after the first bonding step. In this “crack” item, the case where no crack occurs is indicated as “◯”. Further, the “tail joint” item and the “stitch joint” item are items indicating whether or not sufficient joint strength is obtained in the tail portion T and the stitch portion S shown in FIG. 8 after the second bonding step. In these “tail joint” item and “stitch joint” item, “◯” indicates a case where sufficient joint strength is obtained.

  As shown in FIG. 10, in Comparative Examples 1 and 2, sufficient bonding strength could not be obtained in the tail portion T and the stitch portion S after the second bonding step. In Comparative Examples 3 to 6, cracks occurred in the Al wire W after the first bonding step.

  On the other hand, in Examples 1 to 5, no crack was generated in the Al wire W after the first bonding step, and sufficient bonding strength was obtained in the tail portion T and the stitch portion S after the second bonding step.

  From these results, it is preferable that the uneven shape in the chamfered portion 40 has a skewness Rsk of −0.164 or less and an average height Rc of 0.035 μm or more and 0.092 μm or less. Moreover, it is preferable that the uneven | corrugated average height Rc in the press surface 30 is 0.113 micrometer or more.

  When the unevenness skewness Rsk in the chamfered portion 40 is less than −1.4, it is difficult to make the average height Rc of the chamfered portion 40, for example, 0.035 μm or more on the processing principle. Therefore, the unevenness skewness Rsk in the chamfered portion 40 is preferably −1.4 or more.

  The average height Rc of the concavo-convex shape on the pressing surface 30 can be 4.642 μm or less. When the average height Rc of the concavo-convex shape on the pressing surface 30 is higher than 4.642 μm, the concavo-convex shape having an average height Rc of 0.092 μm or more may remain in the chamfered portion 40 after the chamfered portion 40 is formed. Therefore, the average height Rc of the concavo-convex shape on the pressing surface 30 is preferably 4.642 μm or less. In addition, the average height Rc4.642 μm of the uneven shape in the pressing surface 30 is a lower limit value 4.55 μm (see FIG. 11) of the radius of curvature of the chamfered portion 40 and an upper limit value of the average height Rc of the uneven shape in the chamfered portion 40. It is derived by adding 0.092 μm (see FIG. 10).

  The uneven shape on the pressing surface 30 is formed by, for example, sandblasting. When the uneven shape on the pressing surface 30 is formed by sandblasting, the average height Rc of the uneven shape on the pressing surface 30 can be set to 0.45 μm. When the average height Rc of the concavo-convex shape of the pressing surface 30 is formed to exceed 0.45 μm, for example, the ceramic particles on the surface may be deficient (particle dropout). Therefore, the average height Rc of the concavo-convex shape on the pressing surface 30 is more preferably 0.45 μm or less.

  FIG. 11 shows the evaluation results of each item of “crack” and “wire separation failure” when the curvature radius of the chamfered portion 40 is changed.

  Here, the “crack” item is the same item as the “crack” item shown in FIG. Further, the “wire division failure” item is an item indicating whether or not the Al wire W has been appropriately divided after the second bonding step. In this “wire splitting failure” item, the case where no splitting failure of the Al wire W occurs is “◯”.

  As shown in FIG. 11, in Comparative Examples 7 and 8, cracks occurred in the Al wire W after the first bonding step. Moreover, in the comparative example 9, the division failure of the Al wire W occurred after the second bonding process.

  On the other hand, in Examples 6 to 10, no crack was generated in the Al wire W after the first bonding step, and no defective separation of the Al wire W occurred even after the second bonding step.

  From this result, it is preferable that the radius of curvature of the chamfered portion 40 is 4.55 μm or more and 20.3 μm or less.

FIG. 12 is a diagram illustrating an evaluation result of the “crack” item when the curvature radius of the chamfered portion 40 is changed.
Evaluation was performed for the case where the loop length between the first bonding point (for example, a point on the lead electrode 100) and the second bonding point (for example, a point on the pad electrode 200) is 3 mm or more. Here, the loop length is the length of an imaginary line connecting the center lines of both joints. In such a package having a relatively long loop length, the tension applied to the Al wire W is increased in the loop forming process, and cracks are more likely to occur.

  In FIG. 12, the “crack” item is the same item as the “crack” item shown in FIGS.

As shown in FIG. 12, in Comparative Example 10, cracks occurred in the Al wire W after the first bonding step.
On the other hand, in Examples 11 to 13, no crack was generated in the Al wire W after the first bonding step.
From this result, it is preferable that the radius of curvature of the chamfered portion 40 is 12.8 μm or more and 20.3 μm or less.
Thereby, even if the loop length between the bonding point of the first bonding, the second bonding, and the bonding point is 3 mm or more, the occurrence of cracks in the Al wire W can be suitably suppressed. In addition, it is possible to suitably suppress the occurrence of defective bonding of the bonding wire after the second bonding process.

FIG. 13 is a diagram showing the evaluation result of the “crack” item when the taper angle θ1 (see FIG. 3) of the tapered hole 20 is changed.
The taper angle θ1 defines the angle θ2 of the boundary corner portion 50 between the insertion hole 11 and the tapered hole 20. When the taper angle θ1 is relatively large, the angle θ2 of the boundary corner portion 50 is relatively small. Therefore, if the taper angle θ <b> 1 is too large, for example, a crack occurs in a portion of the Al wire W that is in contact with the boundary corner portion 50.

  In FIG. 13, the “crack” item is an item indicating whether or not a crack has occurred in the portion of the Al wire W that has been in contact with the boundary corner portion 50 after the first bonding process. In this “crack” item, the case where no crack occurs is indicated as “◯”.

As shown in FIG. 13, in Comparative Examples 11 and 12, since the taper angle θ1 of the tapered hole 20 was too large, a crack occurred in the Al wire W after the first bonding step. On the other hand, in Examples 14 and 15, no crack occurred in the Al wire W after the first bonding step.
From this result, the taper angle θ1 of the tapered hole 20 is preferably 100 ° or less.
Thereby, generation | occurrence | production of the crack to the Al wire W can be suppressed suitably.

  The taper angle θ1 of the tapered hole 20 is preferably 0 ° or more. When the curvature radius of the chamfered portion 40 is set to a predetermined value (for example, 4.55 μm or more, 20.3 μm or less, or 12.8 μm or more and 20.3 μm or less), the taper angle θ1 of the tapered hole 20 is 0 °. Or even if it is a case close | similar to 0 degree, generating a crack in the part which contact | abutted the chamfer 40 in the Al wire W is suppressed.

  At the time of bonding, energy for joining the Al wire W and the lead electrode 100 is generated at the boundary surface between the Al wire W and the lead electrode 100 (hereinafter simply referred to as “boundary surface”). The energy distribution affects the bonding strength.

FIG. 14 is a schematic perspective view showing an example of a simulation result at the time of bonding. FIG. 15 is a schematic plan view illustrating an example of a simulation result of energy distribution during bonding.
FIG. 16 is a diagram illustrating an evaluation result of the “joining strength” item when the wire diameter Dw and the pressing surface outer diameter Dp are changed.
FIG. 14 is a view of the joint portion as viewed obliquely from below. In the example shown in FIG. 14, the boundary surface is substantially elliptical. In FIG. 14, the energy distribution obtained by the simulation is contour-displayed on the boundary surface.

  For example, the energy distribution changes by changing the ratio Rd (= Dp / Dw) between the pressing surface outer diameter Dp (see FIG. 3) and the wire diameter Dw (see FIGS. 7 and 8). Here, as shown in FIG. 3, the pressing surface outer diameter Dp is an imaginary circle Cr formed by intersecting the extended surface of the outer peripheral surface of the bottle neck portion 14 and the plane including the end portion of the tapered hole 20. Is the diameter.

FIG. 15A shows a simulation result when the ratio Rd between the wire diameter Dw and the pressing surface outer diameter Dp is less than 6 times. FIG. 15B shows a simulation result when the ratio Rd between the wire diameter Dw and the pressing surface outer diameter Dp is 6 times or more.
FIG. 15A and FIG. 15B show half of the energy distribution.

  The item “stitch bonding” in FIG. 16 is an item indicating whether or not sufficient bonding strength is obtained in the stitch portion S illustrated in FIG. 8 after the second bonding process. In the “stitch joint” item, “◯” indicates a case where sufficient joint strength is obtained. The average height Rc of the concavo-convex shape on the pressing surface 30 of the specimen used for this evaluation is 0.20 μm or more and 0.23 μm or less.

  As shown in FIG. 13, in Comparative Examples 13 and 15 having a relatively large ratio Rd, a predetermined bonding strength cannot be obtained. This is because the area of the pressing surface 30 is too large with respect to the wire diameter Dw, and the amount of energy generated per unit area generated on the boundary surface is small. In this case, the predetermined bonding strength cannot be obtained, and the Al wire W may peel from the lead electrode 100 at the boundary surface.

On the other hand, even in Comparative Example 14 in which the ratio Rd is relatively small, a predetermined bonding strength cannot be obtained. This is because the area of the pressing surface 30 is too small with respect to the wire diameter Dw, and a sufficient bonding area cannot be obtained.
On the other hand, in Examples 16 to 19, the ratio Rd is not less than 4.0 times and not more than 5.7 times. In Examples 16-19, desired joining strength is obtained.
From the above results, the ratio Rd is preferably 4.0 times or more and 5.7 times or less.
Thereby, desired joining strength is obtained.

(Production method)
Next, an example of a method for manufacturing the capillary 1 according to the present embodiment will be described with reference to FIG. FIG. 17 is a flowchart illustrating a part of the manufacturing method of the capillary 1. FIG. 17 shows a procedure for forming the chamfered portion 40 and a procedure for forming an uneven shape on the pressing surface 30 and the chamfered portion 40 in the method for manufacturing the capillary 1.

  As shown in FIG. 17, first, the chamfered portion 40 is formed at the boundary portion by performing an R chamfering process on the boundary portion between the pressing surface 30 and the tapered hole 20 (step S101). The R chamfering process is performed by brush polishing, for example. The conditions for brush polishing include, for example, polishing pressure and polishing time. By optimizing these conditions, the chamfered portion 40 having a desired radius of curvature can be formed.

  Subsequently, an uneven shape is formed on the surfaces of the pressing surface 30 and the chamfered portion 40 by subjecting the pressing surface 30 and the chamfered portion 40 to sandblasting (step S102).

  Subsequently, by brushing only the chamfered portion 40, the sharpness of the convex portion 41 in the concave and convex shape of the chamfered portion 40 is made smaller than the sharpness of the convex portion 31 in the concave and convex shape of the pressing surface 30 (step S103). . Thereby, the chamfered portion 40 is provided between the pressing surface 30 and the tapered hole 20, and the capillary 1 having a fine uneven shape on the surface of the pressing surface 30 and the chamfered portion 40 is manufactured.

  In addition, the procedure of the manufacturing method mentioned above is an example, and you may form the chamfer 40 and uneven | corrugated shape by another procedure. For example, both the pressing surface 30 and the chamfered portion 40 may be brush-polished after performing sandblasting in step S102 and before brushing only the chamfered portion 40 in step S103. Thereby, on the surfaces of the pressing surface 30 and the chamfered portion 40, the protrusions 31 and 41 have a concavo-convex shape in which the area of the tip portion is larger than the area of the bottom portion of the recesses 32 and 42, in other words, the sharpness of the protrusions 31 and 41. An uneven shape whose degree is smaller than the degree of sharpness of the recesses 32 and 42 can be reliably formed. In addition, you may perform brush grinding | polishing with respect to the press surface 30 and the chamfering part 40 after step S103.

(Modification)
In the above-described embodiment, a so-called bottleneck type bonding capillary has been described. However, the bonding capillary disclosed in the present application does not necessarily need to be a bottleneck type bonding capillary. For example, it may be a normal type bonding capillary that does not include a bottleneck portion, that is, the tip portion is not sharply cut.

  Moreover, although embodiment mentioned above demonstrated the example in case an uneven | corrugated shape is formed in a press surface and a chamfer part, it is not necessarily required that an uneven | corrugated shape is formed in a press surface. In addition, an uneven shape may be formed in the chamfered portion and the tapered hole.

  In the above-described embodiment, the case where the pad electrode of the semiconductor chip and the lead electrode of the lead frame are electrically connected has been described as an example. However, the bonding capillary disclosed in the present application is not a target other than the above. On the other hand, the present invention can also be applied when bonding wires are bonded.

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

W Al wire T Tail portion S Stitch portion Cr Virtual circle Dp Pressing surface outer diameter Dw Wire diameter 1 Bonding capillary 11 Insertion hole 12 Cylindrical portion 13 Conical portion 14 Bottle neck portion 20 Tapered hole 30 Pressing surface 40 Chamfered portion 50 Boundary corner portion 100 Lead electrode 200 Pad electrode

Claims (1)

A pressing surface for pressing the bonding wire;
An insertion hole through which the bonding wire is inserted;
A taper-shaped hole that communicates the insertion hole and the pressing surface and widens toward the pressing surface;
A chamfered portion provided between the tapered hole and the pressing surface,
The chamfered portion is
A bonding capillary characterized by having a concavo-convex shape on a surface, and a degree of sharpness of a convex portion in the concavo-convex shape being smaller than a degree of sharpness of a concave portion in the concavo-convex shape.